Merck & Co. (MRK)’s experimental insomnia drug, designed to turn off wakefulness rather than subdue the brain into slumber like Ambien, may only be safe at lower doses than what the company has proposed, U.S. regulators said. Doses that Merck studied of as much as 40 milligrams of the drug suvorexant, while effective in helping the sleep deprived, may not be safe, Food and Drug Administration staff said today in a report. Lower doses may work just as well with better safety, but more information may be needed, the staff said. “The lowest strength proposed for marketing by the sponsor is 15 mg,” staff wrote. “If a dosage strength lower than 15 mg is unavailable, we would need to consider if the drug could be marketed safely at all, if we believe that a substantial proportion of the indicated population needs a lower dose.”